1. Field of the Invention
This invention relates to the use of a combination of selected substances in paint to simultaneously prevent the settlement and growth of different bio-fouling organisms, such as barnacles and algae.
2. Description of the Related Art
Biological growth (or bio-fouling) on marine installations and ships constitutes a significant problem for the shipping industry and for owners of marine installations and boats and ships at large. An untreated ship hull will rapidly accumulate fouling of marine plants and animals, which considerably increases hull-to-water friction and consequently, fuel consumption. Also other marine industries and installations, e.g., aqua culture equipment and oil/gas off-shore installations and plants have significant problems with marine bio-fouling.
One way of preventing marine bio-fouling is to apply paint with toxic contents, e.g. tributyltinnoxide (TBT) or copper. The use of marine paints with such contents has, however, proven to cause significant harm to the marine ecosystem including plants, animal species and humans. (1, 2). As used herein, numbers in parentheses refer to references in the list of references herein according to standard practice. Many countries and international organizations have therefore introduced restrictions and prohibitions over their use, and further restrictions are expected. Sale and application of TBT antifouling is to cease, under the International Maritime Organization (IMO) Antifouling System Convention agreed in October 2001. The treaty calls for the ban on application from the first of January 2003, and total prohibition on hulls by the first of January 2008.
It is therefore of interest to find new solutions to prevent marine bio-fouling, to be able to reduce levels of metal and metal-oxides in paints and eventually replace them completely (3-5).
Mechanical cleaning of marine surfaces has been introduced as an alternative to toxics and biocides. Notably, water jet cleaning and mechanical cleaning using brushes are in use. Most of these methods are work-intensive, however, and are therefore expensive.
The tributyltin-ban (TBT) is a reality since the international paint companies have excluded TBT-containing paints from their product portfolio. Instead, the basic biocides are copper, copper oxide or other copper based formulations. When the copper compounds are used in reduced concentrations for ecological reasons, however, these paints need booster biocides against barnacles and algae to achieve a performance acceptable for ship owners and other types of marine industries. Also, paints with specific new compounds active mostly against barnacles, such as medetomidine (“Catemine 1”) as described below, will need a complementary booster compound against algae.
Along the Swedish west coast as well as along the coasts of the North Atlantic Ocean, barnacles and different kinds of algae are particularly apparent problems. The fully grown barnacle is a stationary crustacean, characterized by a centimeter-sized cone shape and enclosing layers of calcinous plates. The mechanical strength of the animal's attachment to solid surfaces is very high, and it is therefore difficult to mechanically remove barnacles from solid surfaces. The animal undergoes different development stages as free-swimming larvae, where the last larva stage is referred to as the cyprid stage. The cyprid screens solid surfaces suitable for settling with the help of a nervous protuberance. A “settling-glue” referred to as balanus cement is secreted from specialized glands localized near the protuberance and the animal thereby settles to the solid surface. After settlement the animal undergoes a metamorphosis into an adult and stationary animal. When using an old copper leaking paint with high concentrations of copper, barnacles are one of the first organisms to foul.
Algae are also relatively insensitive to copper and the amount of leaking copper needed to inhibit fouling of algae is high. Therefore, copper-containing marine antifouling paints are “boosted” by some manufacturers with more specific algicides. The algicides inhibit the zoospores from attaching or inhibit photosynthesis. Both methods give the result of reduced algae fouling.
Previously various compounds have been described and used that interfere with nerve signalling or other specific action against the fauna of marine bio-fouling organisms, such as barnacles or tube worms. For example, U.S. Pat. No. 6,762,227 describes the use of medetomidine (Catemine 1) and other substances. Also, Swedish patent application No. 0300863-8 describes the use of spiroimidazoline (Catemine 3) for the same purpose. However, the use of such products has no or very little effect on algae. For example, Catemine 1 (6) has a specific action on barnacle cyprids but no effect of algal growth due to the target protein being lacking within algae. This is true also for other pharmacological acting substances (7-11).
There are several methods to prevent algal growth, among them the use of copper and other metals in fairly high concentrations. Algicides are often invented as herbicides and are photosynthesis-inhibitors such as DIURON™ (3-(3,4-dichlorophenyl)-1,1-dimethylurea) by DuPont Agricultural Products Wilmington, Del., USA and IRGAROL™ 1051 (2-methylthio-4-tert-butylamino-6-cyclopropylamino-s-triziane) by Ciba Inc, Tarrytown, N.Y., USA. A more common strategy is to use fungicides such as zincpyrithione (Zinc, bis(1-hydroxy-2(1H)-pyridinethionato-O,S)—, (T-4)-) by Arc Chemicals Inc and copperpyrithione (Copper, bis(1-hydroxy-2(1H)-pyridinethionato-O,S)—, (T-4)-) by Arc Chemicals Inc, tolylfluanide (N-(Dichlorofluoromethylthio)-N′,N′-dimethyl-N-p-tolylsulfamide) by Bayer Chemicals, Pittsburgh, Pa., USA, diclofluanide (N′-dimethyl-N-phenylsulphamide) by Bayer Chemicals, ZINEB™ (zinc ethylene bisdithiocarbamate) by FMC corp., ZINRAM™ (Zinc bis(dimethylthiocarbamates)) (3-5) by Taminco, or quaternary ammonium compounds. A third strategy is to use toxic compounds but with short half life such as SEANINE™ (4,5-dichloro-2-n-octyl-3(2H)-isothiazolone) by Rohm and Haas Company, Philadelphia, Pa., USA and related compounds (12).
A strategy that has received a lot of attention for several years is to find natural substances that may work as antifoulants in paint. These substances are endogenously produced by different marine invertebrates and algae to protect their own surface from fouling. Several compounds have been isolated and identified and their antifouling activity been measured (4).
There is a need however to find compounds, or a combination of compounds, to be applied in antifouling paint so that such paint is more effective against both types of organisms such as barnacles and algae without having as many negative ecological effects as paint with high levels of metal-compounds.